William, your best bet really is a trip to a good hardware store or home center. There are probably 3 or 4 possible kinds of hangers that will fit your needs and it will be easier if you take a look. One other suggestion is to check an art supply store or a craft store that has a picture framing department. The same hangers used for pictures may be appropriate for your rack. The type of hanger and the attachment type on the hanger have to work together and we don't really know the second part of this. Twenty pounds is not beyond the capacity of many hangers for pictures and some go far above this.
I will say that I sure prefer to try to get at least one fastner into a stud if at all possible. Remember that is is also possible to use different kinds of hangers on either end.